1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor light emitting device, and more particularly to a semiconductor light emitting device manufacturing method which can achieve an improvement in the bonding force of electrodes while reducing the number of photoresist and lithography processes to be carried out, by unifying processes for forming electrode and mesa structures, thereby simplifying those processes.
2. Description of the Related Art
In recent years, display of full range color has been realized in accordance with development of light emitting devices capable of emitting blue, green, and ultraviolet rays, utilizing a gallium nitride (GaN)-based compound semiconductor.
GaN-based compound semiconductor crystals may be grown over an insulating substrate such as a sapphire substrate. For this reason, in the case of a GaN-based light emitting device, it is impossible to arrange an electrode on the back surface of a substrate. Therefore, both electrodes of the light emitting device must be formed at the side of a semiconductor layer grown over the substrate.
To this end, it is necessary to use a process for forming a mesa structure in which its upper clad layer and active layer are partially removed to partially expose the upper surface of a lower clad layer.
Furthermore, it is necessary to provide an additional layer so that an ohmic contact is formed by a typical electrode, because the upper clad layer, which is made of a p type GaN layer, has a relatively high resistance. For example, a transparent electrode made of Ni/Au is formed prior to formation of a bonding electrode on a p type GaN layer, thereby forming an ohmic contact for reducing a forward voltage Vf, as disclosed in U.S. Pat. No. 5,563,422 (Assignee: Nichia Chemical Industries, Ltd.; and Date of Patent: Oct. 8, 1996). For such a transparent electrode, an indium titanium oxide (ITO) film may be used.
Thus, the above mentioned GaN-based semiconductor light emitting device requires complex processes for forming a mesa structure and an electrode structure, because of the insulating property of its substrate for growth of GaN-based crystals. For this reason, there is a difficulty caused by an increase in respective numbers of photoresist processes, photoresist removal processes, and deposition processes to be carried out for formation of the mesa structure and electrode structure. The complexity of such processes may be identified through exemplary processes of FIGS. 1a to 1i. 
FIGS. 1a to 1i are sectional views respectively illustrating processes of a conventional method for manufacturing a GaN-based semiconductor light emitting device.
In accordance with this semiconductor light emitting device manufacturing method, a primary growth process is first carried out to sequentially form, over a sapphire substrate 11, a first conductivity type clad layer 13, an active layer 15, and a second conductivity type clad layer 17, as shown in FIG. 1a. The crystalline semiconductor layers 13, 15, and 17 may be grown in accordance with an appropriate process such as a metal oxide chemical vapor deposition (MOCVD) process.
Thereafter, a process for forming a mesa structure is carried out in order to form bonding electrodes on the upper surface of the first conductivity type clad layer 13, as shown in FIGS. 1b and 1c. In the mesa structure forming process, a photoresist film 21 is first formed on the second conductivity type clad layer 15 at a region other than a region where the second conductivity type clad layer 15 is to be etched, as shown in FIG. 1b. 
Thereafter, the second conductivity type clad layer 17 and active layer 15 are partially etched to partially expose the first conductivity type clad layer 13, as shown in FIG. 1c. Thus, a mesa structure is formed.
After removing the photoresist film 21 used to form the mesa structure, a photoresist film 22 for formation of a transparent electrode is formed on the resultant structure such that the second conductivity type clad layer 17 is partially exposed at its upper surface, as shown in FIG. 1d. The second conductivity type clad layer 17 is covered by the photoresist film 22 at its edge portions so that the edge portions are prevented from coming into contact with an electrode to be subsequently formed adjacent to the second conductivity type clad layer 17.
Subsequently, a transparent electrode 18 is formed at a desired region on the second conductivity type clad layer 17 by use of the photoresist film 22, as shown in FIG. 1e. 
Thereafter, a process for forming bonding electrodes 19a and 19b on the transparent electrode 18 and the first conductivity type clad layer 13 is carried out, as shown in FIGS. 1f to 1i. In order to form the first bonding electrode 19a, a photoresist film 23 is formed such that the first conductivity type clad layer 13 is partially exposed, as shown in FIG. 1f. After formation of the first bonding electrode 19a, the photoresist film 23 is removed, as shown in FIG. 1g. Similarly, a photoresist film 24 is formed such that the transparent electrode 18 is partially exposed, in order to form the second bonding electrode 19b, as shown in FIG. 1h. After formation of the second bonding electrode 19b, the photoresist film 24 is removed, as shown in FIG. 1i. 
Thus, it is necessary to perform the photoresist process and photoresist removal process four times for formation of the mesa structure, transparent electrode, and first and second bonding electrodes, respectively, in order to form a GaN-based semiconductor light emitting device. Furthermore, each process is complex because it involves a separate deposition process. Additionally, a process for forming a passivation layer is involved in the practical fabrication of semiconductor light emitting devices. For this reason, one photoresist process and one photoresist removal process are required, as shown in FIGS. 2a and 2b. 
In accordance with a conventional process for forming a passivation layer of a semiconductor light emitting device, a passivation layer 20 made of SiO2 or SiN is formed over the light emitting structure obtained after completion of the process shown in FIG. 1i, as shown in FIG. 2a. Thereafter, a photoresist film 25 is formed on the passivation layer 20 such that it does not cover regions where the bonding electrodes 19a and 19b are formed, as shown in FIG. 2b. The passivation layer 20 is then selectively removed, using the photoresist film 25 as a mask, thereby exposing the bonding electrodes 19a and 19b, as shown in FIG. 2c. 
Thus, it is necessary to perform the photoresist process, the photoresist removal process, and the cleaning process five times, respectively, in order to complete a GaN-based semiconductor light emitting device. Such an increased number of photoresist processes to be carried out results in a complexity of the whole process. Furthermore, there is an increased possibility of residual foreign matters after the removal of the photoresist film. The residual foreign matters may degrade the characteristics of the electrode formed in the deposition process.
Moreover, the first and second bonding electrodes must be formed in separate processes using different materials, respectively. For this reason, the number of metal deposition processes for formation of the electrodes is increased, so that the whole process becomes complex.